Workbenches are known which incorporated a top structure comprising a giant vice, for example forming the subject of British Pat. No. 1,267,032 corresponding to U.S. Pat. Nos. 3,615,087 and 3,841,619. Such giant vices comprise a pair of elongate vice beams forming the complete work surface of the workbence and which can be shifted relatively to one another in the manner of a vice by means of a pair of independently operable vice operating screws. This construction is capable of clamping up many different objects of different shapes and sizes both within the clamping gap between the vice members and by means of a number of plug-in abutments received in vertical bores in the vice members.